1. Field of the Invention
This invention relates to an apparatus and method for detecting buried objects using sonic energy.
2. Description of Related Art
The location of underground utilities, and in particular underground gas lines, are not well documented. Often, when digging trenches for new lines or using guided boring for installation of new lines, old utilities are broken. This not only interrupts service but can lead to serious or fatal accidents.
There are two categories of target utilities in the prior art: cooperative targets and uncooperative targets. If an underground utility creates, either artificially or normally, a signal to assist an operator in locating it, the target utility is cooperative. If the underground utility is passive, it is uncooperative. This invention is applicable to either cooperative or uncooperative targets but is particularly suited for uncooperative targets. Generally, the utility line may be metallic or plastic. This invention addresses both metallic and plastic utility lines.
If the utility line is metallic, a metal detector may be used. For shallow, large diameter metal pipe, the metal detector is quite effective. If the metal pipe has a small diameter and is deep, then it usually escapes detection. The sensitivity of metal detectors decreases with the inverse 6th power of distance. This means that if any particular pipe moves twice as far from the metal detector, the signal decreases by {fraction (1/64)} and at 4 times the distance, the signal decreases by {fraction (1/4096)}. It is this sharp decrease in sensitivity with distance that limits the usefulness of metal detectors. Metal detectors do not detect non-metallic pipe or objects.
Ground Penetrating Radar (GPR) may be used to detect both metallic and non-metallic utilities. GPR uses microwave signals to detect such utilities. When GPR is properly used to detect utilities in soils that are relatively transparent, it can be quite effective. The problem with GPR is that there are vast regions, such as most or all of the State of Texas, where the soil is too opaque for microwave penetration by GPR to function. Moisture also attenuates microwave signals. Soils that can be penetrated with microwaves when dry become opaque after a rain.
A microwave transducer need not have intimate contact with the ground when obtaining measurements thereby allowing microwave transducers to be moved over soil at walking speeds. Another advantage of microwaves is that microwave signals propagate mainly in a transverse mode.
According to available information, a large percentage of soils are transparent to sonic signals. As such, this invention utilizes sonic energy in lieu of GPR (microwave signals) or metal detectors to locate underground utilities.
It is one object of this invention to detect, identify and/or map underground obstacles such as buried foundations, tanks, or other objects.
It is another object of this invention to provide a device that detects, identifies and/or maps underground obstacles using sonic signals.
It is another object of this invention to provide a device that utilizes an array of transducers positioned at a fixed position with respect to one another.
According to one preferred embodiment of this invention for mapping three-dimensional images, a device for detecting utilities buried in the ground preferably includes an array of sonic receivers arranged in rows and ranks and positioned against the ground and a corresponding array of sonic transmitters positioned against the ground and connected with respect to and interposed within the array of sonic receivers, each sonic transmitter of the corresponding array of sonic transmitters positioned equidistant from each directly adjacent sonic receiver of the array of sonic receivers.
Alternatively, in a preferred embodiment of this invention for mapping two-dimensional images, a linear array of sonic transmitters is positioned against the ground and a corresponding linear array of sonic receivers positioned against the ground and connected with respect to the linear array of sonic transmitters, each sonic receiver of the corresponding linear array of sonic receivers positioned a distance from each sonic transmitter of the linear array of sonic transmitters, the distance between each corresponding sonic receiver and sonic transmitter being equal.
The device according to this invention may additionally include a signal generator for producing a signal based upon an echo pattern between the array of sonic receivers and the corresponding array of sonic transmitters. In addition, the array of transducers may be positioned in communication with an amplifier for amplifying echoes generated by the array of sonic transmitters; a processor for processing the echoes into echo patterns; and/or a display for displaying the resultant echo patterns.